1. Field of the Invention
The disclosure relates to devices and methods for removing tissue from body passageways, such as removal of atherosclerotic plaque from arteries, utilizing a rotational atherectomy device. In particular, the disclosure relates to improvements in a rotational atherectomy device having an exchangeable drive shaft.
2. Description of the Related Art
A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaque in a patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (i.e., under the endothelium) of a patient's blood vessels. Very often over time what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Several kinds of atherectomy devices have been developed for attempting to remove some or all of such stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (Auth), a rotating burr covered with an abrasive cutting material, such as diamond grit (diamond particles or dust), is carried at the distal end of a flexible, rotatable drive shaft.
U.S. Pat. No. 5,314,438 (Shturman) shows another atherectomy device having a rotatable drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged diameter section being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery.
U.S. Pat. No. 5,314,407 (Auth) shows details of a type of handle which may be used in conjunction with rotational atherectomy devices of the type shown in the Auth '134 and Shturman '438 patents. A handle of the type shown in the Auth '407 patent has been commercialized by Heart Technology, Inc. (Redmond, Wash.), now owned by Boston Scientific Corporation (Natick, Mass.) in the rotational atherectomy device sold under the trademark Rotablator®. The handle of the Rotablator® device includes a variety of components, including a compressed gas driven turbine, a mechanism for clamping a guide wire extending through the drive shaft, portions of a fiber optic tachometer, and a pump for pumping saline through the drive shaft.
The connection between the drive shaft (with its associated burr) and the turbine in the Rotablator® device is permanent; yet, frequently it is necessary to use more than one size burr during an atherectomy procedure. That is, often a smaller size burr is first used to open a stenosis to a certain diameter, and then one or more larger size burrs are used to open the stenosis further. Such use of multiple burrs of subsequently larger diameter is sometimes referred to as a “step up technique” and is recommended by the manufacturer of the Rotablator® device. In the multiple burr technique it is necessary to use a new Rotablator® device for each such successive size burr. Accordingly, there is a need for an atherectomy system that would permit a physician to use only one handle throughout an entire procedure and to attach to such handle an appropriate drive shaft and tissue removing implement (e.g., a burr) to initiate the procedure and then exchange the drive shaft and the tissue removing implement for a drive shaft having a tissue removing implement of a different size or even a different design.
A subsequent version of the Rotablator® has been introduced with the ability to exchange a flexible distal portion of the drive shaft together with a burr for another distal portion of a drive shaft having a different size burr. Technical details of such a system are contained in U.S. Pat. No. 5,766,190, titled “Connectable driveshaft system”, and issued on Jun. 16, 1998 to Wulfman. This system utilizes a flexible drive shaft having a connect/disconnect feature allowing the physician to disconnect the exchangeable distal portion of the flexible drive shaft together with the burr from the flexible proximal portion of the drive shaft which is connected to the turbine of the handle, thus permitting the burr size to be changed without discarding the entire atherectomy unit. Each exchangeable drive shaft portion is disposed within its own exchangeable catheter and catheter housing. The flexible proximal portion of the drive shaft in this system is permanently attached to the turbine and is not exchanged. This system has been commercialized by Boston Scientific under the trademark Rotalink System®. While the Rotalink System® does permit one to change the burr size, the steps required to actually disconnect the exchangeable portion of the drive shaft and replace it with another exchangeable portion of the drive shaft are quite involved and require relatively intricate manipulation of very small components.
First, a catheter housing must be disconnected from the handle and moved distally away from the handle to expose portions of both the proximal and distal sections of the flexible drive shaft which contain a disconnectable coupling. This coupling is disconnected by sliding a lock tube distally, permitting complementary lock teeth on the proximal and distal portions of the flexible drive shaft to be disengaged from each other. A similar flexible distal drive shaft portion with a different burr may then be connected to the flexible proximal portion of the drive shaft. To accomplish such assembly, the lock tooth on the proximal end of the distal replacement portion of the drive shaft must first be both longitudinally and rotationally aligned with the complementary lock tooth at the distal end of the proximal portion of the drive shaft. Since the flexible drive shaft typically is less than 1 mm in diameter, the lock teeth are similarly quite small in size, requiring not insignificant manual dexterity and visual acuity to properly align and interlock the lock teeth. Once the lock teeth have been properly interlocked with each other, the lock tube (also having a very small diameter) is slid proximally to secure the coupling. The catheter housing must then be connected to the handle housing.
While this system does permit one to exchange one size burr (together with a portion of the drive shaft) for a burr of another size, the exchange procedure is not an easy one and must be performed with considerable care. The individual performing the exchange procedure must do so while wearing surgical gloves to protect the individual from the blood of the patient and to maintain the sterility of the elements of the system. Surgical gloves diminish the tactile sensations of the individual performing the exchange procedure and therefore make such exchange procedure even more difficult.
In recent years, there has been an effort to develop an atherectomy device with easier attachment and/or exchange of the drive shaft and its tissue removing implement.
For instance, U.S. Pat. No. 6,024,749 (Shturman et al), U.S. Pat. No. 6,077,282 (Shturman et al), U.S. Pat. No. 6,129,734 (Shturman et al) and U.S. Pat. No. 6,852,118 (Shturman et al), all incorporated by reference in their entirety herein, disclose an atherectomy device having an exchangeable drive shaft cartridge comprising a housing that is removably attachable to the device's handle housing. The exchangeable cartridge includes a longitudinally movable tube that is removably attached to the prime mover carriage and a rotatable drive shaft that is removably attachable to the prime mover. A coupling is provided which connects the longitudinally extendible tube to the prime mover while indexing the relative position of the longitudinally extendible tube and the proximal portion of the drive shaft. U.S. Patent Publication No. 2011/0087254 (Welty), incorporated by reference in its entirety herein, discloses an atherectomy device where the prime mover has a prime mover coupler and the drive shaft has a drive shaft coupler that is engageable with the prime mover coupler. The drive shaft coupler and prime mover coupler have engageable lateral cross-sections that are complementary and geometrically keyed to one another. When they are engaged to one another, the complementary cross-sections allow axial translation between the drive shaft coupler and the prime mover coupler while prohibiting rotational coupler between the drive shaft coupler and the prime mover coupler.
Other atherectomy devices, such as U.S. Patent Pub. No. 2011/0077673 (Grubac et al), utilize a magnetic clutch connection between the drive shaft and the prime mover. The drive shaft and the prime mover are held together longitudinally by a magnetic attractive force between the motor plate and the drive shaft plate. The torques between the motor and the drive shaft are transmitted completely between the motor plate and the drive shaft plate and, when below a threshold torque, the motor plate and the drive shaft plate remain held together rotationally by static friction. When the torques between the motor and the drive shaft are greater than the threshold torque, the motor plate and the drive shaft plate slip rotationally past each other, causing a residual torque to be transmitted between the motor and the drive shaft.
Although the above devices utilize friction or magnetic couplings to removably engage the drive shaft with the prime mover, some atherectomy devices have a driveshaft driven by a pair of mating gears, one gear connected to the drive shaft and one gear connected to the mating gear. Due to this gearing arrangement, the atherectomy device is generally restricted to one shaft size per assembly. Typically the gear connected to the drive shaft is not replaced, so any exchangeable drive shaft must be sized to properly engage with the drive shaft. Thus, multiple atherectomy devices are needed for each desired drive shaft diameter.
Accordingly, there exists a need for an atherectomy device with the mating gear assembly where the drive shaft is exchangeable for another drive shaft of either the same size or another size.